| Author |
Message |
MC - Iv (24.83.235.106)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 01, 2002 - 2:50 am: | |
I recently completed an air brake course and I passed the appropriate tests in order to get an air brake endorsment on my driver's licence. I highly recommend it to amateurs like myself. The information was invaluable.
My question is this: My MC-9 doesn't appear to have "spring brakes" on the drive axle. "Da book" doesnt explain the locking mechanism in the brake chambers very well. Can anyone desribe briefly how the park/emergency brake works?
Iv. |
jim (209.240.222.32)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 01, 2002 - 6:43 am: | |
there are parking brakes on the mci-9 rear driving axle.... they are the "roto-chamber" kind... a proprietary type used on mci coaches.... they do work sort of like a 30/30 brake chamber(spring brake chamber).. but in addition to the valve next to the shifter, require that the coach operator apply the foot brake one time to release .... the normal spring brake chambers release by a valve on the dash... both systems use air to release the park brake... and use a spring force to hold the brakes applied.... |
Jim Ashworth (Jimnh) (172.133.144.21)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 01, 2002 - 8:51 am: | |
Sorry, but that's dead wrong. The MCI's use a Bendix DD-3 chamber that has no spring. Service brakes are activated by applying air to one of the diaphragms. Parking brakes are activated by applying air to the other diaphragm. In order to keep the parking brakes on should air leak out, there is a tapered cone with balls that are surrounding the shaft that goes to the slack adjuster. Should air fail, these balls are jambed between the taper and the shaft, effectively locking the brakes on. This is why, if the parking brakes are applied and released shortly after, you don't have to make a service brake application to release the parking brake. If, on the other hand, the air is lost from the parking chamber, the balls lock and it requires a service brake application to move the shaft sufficiently to un-jamb the balls so the shaft can release. This is a little simplified because there are more things going on in the "can" than I have mentioned but it will give you an idea of what is happening. Da Bendix book does have the answers.
Jim |
Stephen Fessenden (Sffess) (63.27.88.6)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 01, 2002 - 8:21 pm: | |
DD3s can fail, rarely. I had a rusty bus that did not hold the parking brake locked when the air pressute bled down. The above mentioned tapered cone system was too rusty. Test occasionally by trying to drive off with the parking brake on after air pressure has bled down. Better to test in flatland than on a steep grade in the middle of a trip.
It was not expensive to fix. The mechanic rebuilt the drive axle air chambers and cleaned up the mechanical locking mechanism. They worked great. |
Ear-8-Ky. (209.42.178.249)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 02, 2002 - 10:50 am: | |
Sorry Jim but I have a 76 MC8 that has spring brakes. The service manual even tells about them. Everyone that I know of that has a MCI has spring brakes. |
DaveD (216.18.113.69)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 02, 2002 - 1:26 pm: | |
Mine doesn't
DaveD |
Jim Ashworth (Jimnh) (172.142.158.226)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 02, 2002 - 6:34 pm: | |
The genuine MC-8 Service Manual makes no mention of anything but DD-3 brakes for the 8's. The original mid '70s vintage MCI parts manual also has no reference to anything but DD-3 brakes. You may have them, I wouldn't doubt that, but I think your bus is in the minority with the spring brakes. As an aside, NJ and MA busses were required to have DD-3 brakes as well as the primitive anti-lock systems which were quickly disabled with the State's blessing since it was a catastrophic attempt to promote braking safety.
Jim NH |
Jim Nelson (65.56.69.93)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 05, 2002 - 8:58 pm: | |
The new 2001 D4500's have spring brakes, as well as the G4500, and MCI built 2 test MC-12's with Dana axles, 50 series engines, and spring brakes. Everything before that had DD3 brakes - to the point that many Greyhound mechanics don't even remember how to cage a spring brake! I'm glad to see those antiquated, balky systems go away - MCISP wants $700 for a rebuilt one, and we normally replace 2-4 a week. |